I just treated one of my sleeves on my 1401 with ELC's conditioner a couple of days ago, very happy with the result (tried to loosen up the leather a bit). Have never used anything else but I'm sure many of the other brands out there which have been discussed work just as well.
RM Williams Saddle and Leather Dressing. Been using it for years and easily the best stuff I have found by a very long chalk. I use it on boots, bags, you name it. Doesn't and won't go rancid like some natural dressings. Wouldn't buy anything else.